GPX3 and infection: The tissue selenium concentration increases at a lower rate to the normal level compared with the plasma concentration and it begins to increase after selenium supplementation for 2 days and then continues to increase slowly for several weeks [43].Therefore, it makes sense that selenium supplementation slowly increases the intracellular concentration of selenium and the activity of glutathione peroxidase-3, an enzyme that prevents the damaging of endothelial cells and the adherence of bacteria into the respiratory mucosal cells and thereby infection.